Dave Storrs <[EMAIL PROTECTED]> writes:
> On Wed, Dec 18, 2002 at 09:31:41AM +0000, Piers Cawley wrote:
>> Dave Storrs <[EMAIL PROTECTED]> writes:
>> > It seems like Perl6 is moving farther and farther away from Perl5's
>> > (almost) typelessness.
>>
>> It depends what you mean by typed. Perl has always had strongly typed
>> *values* (which strike me as being a damn sight more useful than
>> typed variables).
>
> No argument from me. When I want/need the abilities that come with
> specifying type, I want the language to support it. I just don't want
> to _have_ to do it, when I don't want/need those abilities.
>
>
>>In a language with typed values, being able to
>> declare a typed variable is useful for a few reasons:
>>
>> * After watching things in a profiler, you sacrifice programmer
>> flexibility by typing a couple of variables as a way of giving the
>> Optimizer something to get its teeth into (if you have a typed
>> variable then you can limit the amount of runtime checking you have
>> to do in favour of compile time checks)
>
> Agreed.
>
>
>> * For setting up multiply dispatched methods and functions. Consider
>> the example below (which I know I've used before).
>>
>> sub grep ( (Rule | Block) $selector, @*args ) { @args.grep($selector) }
>> sub grep ( (Rule | Block ) $selector, Collection $collection ) {
>> $collection.grep($selector)
>> }
>>
>> sub grep ( WeirdSelector $selector, @*args ) {
>> grep $selector.as_block, *@args;
>> }
>>
>> Because we can declare the types of the function parameters we can
>> let the language sort out the dispatch for us. Without typed
>> parameters and multi dispatch those three function definitions
>> become:
>>
>> sub grep ( $selector, $first, @*args ) {
>> if @args.length {
>> return [ $first, @args ].grep($selector);
>> }
>> else {
>> $first.grep($selector);
>> }
>> }
>>
>> method Object::grep ($self: $selector {
>> [ $self ].grep($selector);
>> }
>
> Hm. I'm way short on sleep today, so I'm probably missing something,
> but I don't see why Perl can't sort this out without a specific
> typing.
Well, you've got to specify the types *somewhere* when you set up
your multimethods. The parameter list seems a better place than most.
> On a more nit-picky level, the first two subs in the top block seem to
> show that arrays are not derived from Collection. Surely, if
> everything is an object, they should be?
They are, but that C<< @*ary >> is *not* the same as C<< @ary >> in
an arg list, it flattens the remaining arguments into an array, on
which we then call the grep method. Essentially the variant is only
there to normalize the list of arguments.
